Heretofore, there has been known one type of digital measurement apparatus which comprises data capture means operable to continuously capture digital data about a target measurement item, validity determination means operable to compare the captured data with a reference value so as to determine whether all of the captured data are valid, and measurement-value calculation means operable, when all of the captured data are determined to be valid, to calculate a measurement value in accordance with the valid data. Such a digital measurement apparatus includes various digital weight measurement apparatuses targeting at an object's weight as a measurement item, and various body-composition measurement apparatuses targeting at a user's body composition, such as body fat percentage, visceral fat level, muscle mass, estimated bone mass or basal metabolic rate, as a measurement item.
Among the digital weight measurement apparatuses, a conventional digital body-weight measurement apparatus targeting at a user's body weight is generally designed as follows. When a user steps onto a loading board, an electric signal corresponding to a user's body weight is output from a load sensor incorporated in a main unit of the apparatus. This signal is converted to digital data (count values) through a digital conversion circuit incorporated in the main unit. Then, such count values are continuously sent to a calculation device incorporated in the main unit. When given plural number (e.g. eight) of the count values are captured, the calculation device calculates a difference between a maximum one and a minimum one of the count values (or a variation of the count values), and then compares the variation with a predetermined reference value.
In this process, if the variation of the count values is equal to or less than the reference value, it will be determined that all of the captured count values are valid, or the user is on the loading board in a stable measurement posture in view of a small variation in a load imposed on the loading board. Then, the calculation device calculates a measurement value or a body-weight value in accordance with the captured count values at the time when they are determined to be valid. More specifically, the calculation device converts an average value of the eight count values to a measurement value or a body-weight value, and displays the body-weight value on a display device, such as LCD, incorporated in the main unit.
When the variation of the count values is greater than the reference value, one count value is additionally captured, and the oldest one of the eight previously captured count values is substituted with the latest count value. Then, a variation of the eight regrouped count values is calculated, and re-compared with the reference value.
These processes for capturing an additional count value, calculating a variation and comparing with the reference value will be repeatedly performed until a variation of regrouped count values becomes equal to or less than the reference value. This processing using a reference value is widely used in various digital weight measurement apparatuses other than the body-weight measurement apparatus.
The conventional body-composition measurement apparatus targeting at a user's body composition, such as body fat percentage, visceral fat level, muscle mass, estimated bone mass or basal metabolic rate, as a measurement item, is generally designed as follows. A certain current is supplied between two regions of the body of a user to measure a resulting voltage in the body, and a bioelectric impedance value (hereinafter referred to occasionally as “BI value”) of the user is calculated based on the measured voltage. Then, the calculated BI value and a personal parameter of the user typically including body height, body weight, age and sexuality are assigned to a predetermined regression formula to calculate an intended body composition.
For the purpose of calculating a BI value of a user, a main unit of the body-composition measurement apparatus incorporates a group of electrodes and a current-feed circuit for feeding a current between at least two regions of the user's body, and a group of electrodes and a voltage measurement circuit for measuring a voltage to be generated under the current supply depending on an impedance of the user's body.
When the user brings two regions (e.g. right and left feet bottoms) of his/her body into contact with the groups of electrodes, a certain current is fed from the current-feed circuit to the user's body, and an electric signal corresponding to a resulting voltage in the user's body is output from the voltage measurement circuit. This electric signal is converted to a digital signal through an analog-digital conversion circuit incorporated in the main unit, and then continuously sent to a calculation device incorporated in the main unit. In accordance with the received digital signal, the calculation device continuously calculates and captures BI values which are digital data about a body composition or a target measurement item. Then, when the number of captured BI values reaches a given value (e.g. eight), each of the captured BI values is compared with an upper reference value and a lower reference value.
As the result of the comparison, if all of the BI values fall within the range of the upper reference value to the lower reference value, it will be determined that all of the captured BI values are valid, or the user is in a stable measurement posture to maintain an adequate contact between the user's body and the groups of electrodes. Thus, a body composition or a measurement value is calculated based on the BI values at the time when they are determined to be valid. More specifically, an average value of the eight BI values are assigned to the aforementioned regression formula to calculate a value of a body composition, such as body fat percentage or visceral fat level, as a target measurement item, and the calculated body composition value is displayed on a display device, such as LCD, incorporated in the main unit.
When either one of the BI values deviates from the range of the upper reference value to the lower reference value, one BI value is additionally captured, and the oldest one of the eight previously captured count values is substituted with the latest count value. Then, each of the eight regrouped count values is re-compared with the upper reference value and the lower reference value.
These processes for capturing an additional BI value and comparing with the upper reference value and the lower reference value will be repeatedly performed until all of captured BI values fall within the range of the upper reference value to the lower reference value.
Refer, for example, to the following Patent Publications 1 and 2 for the aforementioned digital body-weight measurement apparatus and body-composition measurement apparatus.                [Patent Publication 1] Japanese Patent Laid-Open Publication No. 2002-013976        [Patent Publication 2] Japanese Patent Laid-Open Publication No. 2001-204704        